1. Field of the Invention
The present invention relates to an image forming apparatus and more specifically, to an image forming apparatus including a recording head discharging droplets.
2. Description of the Related Art
The ink-jet recording apparatus and the like are known as an image forming apparatus of a liquid discharging recording type, such as a printer, a facsimile, a copier, a plotter, a multifunction device of them, and the like, using, for example, a recording head that discharges ink droplets. In the image forming apparatus of this liquid discharging recording type, ink droplets are discharged from a recording head to a conveyed paper to form an image (record, type, develop, and print are also used as synonyms.) on the paper. This type includes a serial type image forming apparatus in which droplets are discharged from the recording head with the recording head being moved along a main scanning direction to form an image, and a line type image forming apparatus in which droplets are discharged from a line type recording head that is not moved while forming an image.
Here, in this application, the term “the image forming apparatus” includes an apparatus by which image formation is performed by providing ink on a medium such as a paper, a thread, a fiber, a textile, a leather, a plastic, a glass, a wood material, ceramics, and the like.
Further in this application, the term “the image formation” includes forming a meaningless image such as a pattern or the like on the medium, in other words just providing ink on the medium, in addition to forming an image with some meaning such as characters, drawings and the like on the medium.
Further in this application, the term “the ink” or “the droplet” is used as a generic of liquid capable of forming an image such as recording liquid, fixing treatment liquid, solution, resin, or the like in addition to liquid or a droplet so called as ink.
Further in this application, the term “paper” is used as a generic of material on which an ink droplet is attached and includes the medium mentioned above such as an OHP (overhead projector) sheet, a textile or a cloth, or the like in addition to a typical paper.
Further, the term “an image” includes a three-dimensional image such as an image formed on a three-dimensional body or a stereoscopically formed image of a three-dimensional body in addition to a plane image.
Among the image forming apparatuses of the liquid discharging recording type, there is an apparatus that includes a maintenance and recovery mechanism including a cap member for capping or covering a nozzle surface of a recording head, a wiper member (called also as a wiper blade, a wiping blade, blade and the like) for wiping the nozzle surface of the recording head to clean the surface, and the like. In this apparatus, the maintenance and recovery mechanism performs a recovery operation of wiping the nozzle surface by the wiper member to form a nozzle meniscus after thickened ink is discharged into the cap member.
With this structure, ink is stably discharged from the nozzle of the recording head, evaporation of ink from inside of the nozzle can be prevented, and contamination of the nozzle by dust can be prevented.
Japanese Patent No. 3589238 discloses such the mechanism. Japanese Patent No. 4186557 also discloses a maintenance and recovery mechanism that includes a cap for capping a vertically positioned nozzle surface of a recording head, a release port capable of being open to the air, a suction port, a tube pump connected to the suction port, and a switch valve for opening and closing the release port to the air.
According to this technique, before releasing the cap member after suctioning the vertically positioned nozzle surface of the recording head capped by the cap member by the tube pump, the release port is opened to the air by the switch valve. Then, the liquid pulled down by a force of gravity and gathered at the bottom of the cap member is suctioned by the tube pump. Thereafter, the cap member is released.
However, when the release port is opened to the air after the cap member is suctioned by the pump, because of the air flushed into the cap member, the inside pressure of the cap member becomes drastically high to cause a pressure overshoot. As a result, the liquid gathered at the bottom of the cap member is scattered out of the cap member via the release port and the switch unit. Especially when the pump that blocks the flow of the liquid exhausted from the cap member such as a tube pump is used, this type of problem easily occurs.